I have a stock late model 302 with c4 trans and a holley 4160 4bbl in a 66.I puta vacuum gauge to it to check for lean best idle.What kind of reading should i get and which vacuum port to use.I used the one on the bottom plate in the front.I got something like 20-21.

 

You can use any manifold vacuum port to measure vacuum. If you hook your gauge up to a timed vacuum port, it probably won't (shouldn't) register much of a reading at idle, so you will know that you have the wrong port.

20-21 inches of steady vacuum is a good measurement, usually the higher the better. If it is below 16, or if it drops, or if it fluctuates too much, you know you have a problem. Yours sounds good though.

 

Put the car in drive, with the wheels chocked of course, and adjust your carb. The 20-21 inches is great, but I'll bet it's in neutral. Chances are you're using the correct vacuum port if you get this reading. What you want is manifold vacuum, like NorCalTroy sez.

 

Awesome thanks guys.